1. Field of the Invention
The present invention generally relates to a MEMS structure and a method for making the same. In particular, the present invention relates to an MEMS structure with a 3D diaphragm electrode and a method for making the same. Such 3D diaphragm electrode has a composite structure to enhance the mechanical strength of the 3D diaphragm electrode per se.
2. Description of the Prior Art
MEMS devices include micro machines integrated with electronic micro circuits on substrates. Such devices may form, for example, microsensors or microactuators which operate based on, for example, electromagnetic, electrostrictive, thermoelectric, piezoelectric, or piezoresistive effects. MEMS devices have been formed on insulators or other substrates using micro-electronic techniques such as photolithography, vapor deposition, and etching . . . etc. Recently, MEMS is fabricated using the same types of steps (such as the deposition of layers of material and the selective removal of the layers of material) that are used to fabricate other conventional analog and digital complementary metal oxide semiconductor (CMOS) circuits. An MEMS microphone structure presently can be made from general micro electronic technology, such as photolithography, vapor phase deposition, etching or LIGA, performed on a substrate, such as an insulating layer or other semiconductor.
Referring to FIG. 1 through FIG. 3, FIG. 1 through FIG. 3 are schematic diagrams illustrating a method of fabricating a MEMS microphone structure according to the prior art. As shown in FIG. 1, the method of fabricating the MEMS microphone structure 10 with multi-metal layers according to the prior art is as follows. First, a substrate 12 is provided, and the surface of the substrate 12 has a base sacrificial layer 14 and a first metal layer 16. Then, the first metal layer 16 is patterned to form a first micro-machined metal mesh 18. Next, as shown in FIG. 2, a first sacrificial layer 20 is deposited to cover the substrate 12, and the surface of the first sacrificial layer 20 is planarized. Thereafter, a second metal layer 22 is formed on the first sacrificial layer 20, and then, a second metal layer 22 is patterned to form a second micro-machined metal mesh. Next, a second sacrificial layer 26 is deposited to cover the substrate 12, and the surface of the second sacrificial layer 26 is planarized. Then, a third metal layer 28 is formed on the second sacrificial layer 26, and then, the third metal layer 28 is patterned to form a third micro-machined metal mesh. Later, a third sacrificial layer 32 covers the substrate 12. Finally, as shown in FIG. 3, an isotropic dry etching process is utilized to remove the first sacrificial layer 20, the second sacrificial layer 26, the third sacrificial layer 32 and apart of the base sacrificial layer 14 among the first micro-machined metal mesh 18, second micro-machined metal mesh and third micro-machined metal mesh, so that the first micro-machined metal mesh 18, the second micro-machined metal mesh and the third micro-machined metal mesh are suspended above the substrate 12 so as to form a multilayer membrane. Afterwards, aback side etching process is performed to etch through the substrate 12 so as to allow free movement of air molecules and vibrate the multilayer membrane. Therefore, the MEMS microphone structure 10 according to the prior art is formed.
As described above, the conventional MEMS microphone structure uses a traditional Al process to form the micro-machined metal mesh according to the prior art, that is, the first metal layer, the second metal layer and the third metal layer composed of aluminum are respectively formed first, and then, a photoresist layer is coated thereon. Next, the photoresist layer is patterned, and then, the photoresist layer is used as a mask to etch the metal layers so as to form the micro-machined metal mesh. However, because the above-described method needs to etch multiple layers of metal, a novel micro electro mechanical system (MEMS) structure is still needed to possess a much more robust but simpler structure.